1. Field of the Invention
The present invention relates to the superfine particles of Prussian blue-type complexes, their dispersion liquid, and a fabrication method of these materials, and more specifically relates to the superfine particles of Prussian blue-type complexes with nanometer-scale size, their dispersion liquid, and a fabrication method of these materials.
2. Description of the Related Art
Metal-complexes consisting of the particular metals and particular coordination molecules show various properties depending on the combination of the kind of metals and the kind of the coordination molecules. These materials have a much broader range of applications, for example, drugs, luminescent materials, coating medium, etc.
On the other hand, the fabrication of the superfine particles of bulk materials often drives a novel character that never appears in the bulk. Such an appearance of the novel characters has extensively been studied and used. However, synthesizing superfine particles of the metal complexes have been started only in this decade.
Among the metal-complexes, Prussian blue and its analogues, so-called Prussian blue-type complexes, have extensively been studied. Prussian blue has used as a blue pigment from the 18th century. Furthermore, it has potential applications for displays, smart windows, and biosensors.
FIG. 10 shows the crystal structure of the Prussian blue-type complexes. In the present invention, the crystal of the Prussian blue-type complexes includes the modified structure from the crystal of the Prussian blue, such as the substitution or the defect of the transition metals and hexacyano-metallic group, intercalation of the various ions or waters.
The crystal structure has a three-dimensional network structure with two kinds of metal atoms M1 and M2 with NaCl-type network connected by cyano-groups consisting of the carbon atoms 102 and nitrogen atoms 103. As the metallic atoms M1 and M2, various elements such as Vanadium, Chromium, Molybdenum, Tungsten, Manganese, Iron, Ruthenium, Cobalt, Nickel, Platinum, Copper can be used. Because various character such as magnetism or optical properties by the substitution of the metallic atoms, various kind of materials has been studied (Patent. 1, 2).
In the fabrication of the stable superfine particles of the Prussian blue-type complexes, dispersibility in solvents is very important. If the stable dispersibility of the superfine particles in various solvents, various inexpensive and simple method can be used for fabricating films, such as spin-coating. Then the film will be utilized for various applications such as biosensor.
Therefore, how to fabricate superfine particles is very important for practical application of the Prussian blue-type complexes. There have been a few reports of the method to fabricate superfine particles. In these reports, as the materials for stabilizing superfine-particles, surface active agent such as di-2-ethylhexylsulfosuccinate sodium salt (AOT), polyers as poly(vinylpyrrolidone (PVP), or ferritin proteins were used for (M Yamada, et al.: J. Am. Chem. Soc., 126 (2004) p9482.). But they do not suit for inexpensive and simple mass production because of their complexity of the synthesizing process, their expensive price of the stabilizing molecules, or requirement of enormous volume of solvents.    Reference 1: Japanese Patent Disclosure 2005-3679    Reference 2: Japanese Patent Disclosure Heisei 7-270831
The conventional fabrication method of the superfine-particles such as reversed micelle method limits the kinds of the stabilizing materials that cover the surface of the superfine-particles. The reversed micelle method has three processes, (i) the process of synthesizing the 1st reversed micelle solution of hexacyano metallic complexes (anion) and the 2nd reversed micelle solution of the metal ion solution, (ii) the process of the mixing the 1st reversed micelle solution and the 2nd reversed micelle solution, and (iii) the process of the synthesizing superfine particles by adding molecules to cover the surface (surface-covered molecule) into the mixed solution obtained in the process (ii). In the case of the reversed micelle method, a large amount of the surfactant to form the reversed micelle in addition to the surface-covered molecule is required. A large amount of the organic solvent is also used, resulting in that this method is not inexpensive. Furthermore, this method has less versatility because the kinds of the solvents, surface-covered molecules, and surfactant used in this method are limited due to the requirement of the stable structure of the reversed micelles.